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(Hypertension. 2009;53:338.)
© 2009 American Heart Association, Inc.

Original Articles Part 2

Intrarenal Angiotensin III Infusion Induces Natriuresis and Angiotensin Type 2 Receptor Translocation in Wistar-Kyoto but not in Spontaneously Hypertensive Rats

Shetal H. Padia; Brandon A. Kemp; Nancy L. Howell; John J. Gildea; Susanna R. Keller; Robert M. Carey

From the Division of Endocrinology and Metabolism, Department of Internal Medicine, University of Virginia Health System, Charlottesville.

Correspondence to Shetal H. Padia, PO Box 801414, University of Virginia, Charlottesville, VA 22908-1414. E-mail shp6a{at}virginia.edu

In Sprague-Dawley rats, renal angiotensin (Ang) type 2 receptors (AT₂Rs) mediate natriuresis in response to renal interstitial (RI) D₁-like receptor stimulation or RI Ang III infusion. After D₁-like receptor activation, apical membrane (AM) but not total renal proximal tubule cell AT₂R expression is increased, suggesting that AM AT₂R translocation may be important for natriuresis. The onset of hypertension in spontaneously hypertensive rats (SHRs) is preceded by defects in renal sodium excretion. The present study examines AT₂R-mediated natriuresis in response to RI Ang III infusion in Wistar-Kyoto rats (WKYs) and SHRs. WKYs and SHRs received RI Ang III infusion after 24 hours of systemic AT₁R blockade with candesartan. In WKYs, urine sodium excretion rate increased from 0.043±0.01 to 0.191±0.06 µmol/min (P<0.05) in response to Ang III infusion, but identical conditions failed to increase the urine sodium excretion rate in SHRs. The increase in the urine sodium excretion rate was blocked by coinfusion of PD-123319, a selective AT₂R antagonist. On confocal microscopy images, Ang III–infused WKYs demonstrated greater renal proximal tubule cell AM AT₂R fluorescence intensity compared with SHRs (5385±725 versus 919±35; P<0.0001), and Western blot analysis demonstrated increased AM (0.050±0.003 versus 0.038±0.003; P<0.01) but not total cell AT₂R expression in WKYs. In SHRs, AM AT₂R expression remained unchanged in response to RI Ang III infusion. Thus, RI Ang III infusion elicits natriuresis and renal proximal tubule cell AT₂R translocation in WKYs. Identical manipulations fail to induce natriuresis or AT₂R translocation in SHRs, suggesting that defects in AT₂R-mediated natriuresis and trafficking may be important to the development of hypertension in SHRs.

Key Words: sodium • natriuresis • angiotensin III • AT₂ receptor • AT₁ receptor • translocation